Recently, a three-dimensional package device having a multilayered device structure has been developed. This three-dimensional package device is obtained by stacking silicon substrates or the like having, e.g., circuit elements and memory elements, in multiple levels to form a multilayered substrate, and connecting the layers with through hole interconnections. This structure realizes a compact device having a high space efficiency.
In this three-dimensional package device, interconnection through holes each with a diameter of about 10 μm to 70 μm must be formed in silicon substrates each with a thickness of about 100 μm. Hence, very high-rate etching is required.
High-rate silicon etching can be applied not only to such a three-dimensional package device but also to machining of the order of submicrons in various types of micromachining, and can be utilized to form not only through holes but also, e.g., groove shapes.
For the high-rate etching, an induction coupling type plasma etching apparatus which can realize a high plasma density is conventionally used.
However, even in high-rate etching using the conventional induction coupling type plasma etching apparatus, the etching rate is about 10 μm/min at maximum, and a sufficiently high rate is not always obtained.